The objective of this work is to develop a more complete understanding of the mechanisms involved in genetic recombination. The E. coli genetic system will be used and the problem of recombination mechanism will be approached from the prospective of variations in DNA substrates and the configuration of the recombining DNA molecules. An analysis of the recombination of various pairings of DNA substrates will involve examining both the protein product made from a transcribable DNA structure generated by recombination between two mutant genes and the viable recombinant colonies formed. Both types of recombination assays will be performed in a variety of recombination deficient mutants in order to establish the ability of the putative recombination pathways to initiate and/or complete a recombination event when the nature and configuration of the DNA substrates are varied. The various DNA substrates will be physically characterized in order to ascertain potential correlations between physical structure and recombinogenic potential. The physical studies will include attempts to demonstrate enzymatically produced variations in DNA configuration. Information obtained from these studies will be used to develop a system where in vitro recombination can be examined by measuring a transcribable protein product from two recombining genes.